Tube VCF on Dutch synth forum

etaoin · Joined: Jun 30, 2005 Posts: 761 Location: Utrecht, NL

Jeroen Baars designed a nasty Tube VCF which he posted on the Dutch synth forum, here: http://www.synthforum.nl/forums/showthread.php?t=90425

The final design and sound samples are on his website: http://www.electricdog.eu/

I did a PCB design for it that might be interesting to some of you out here:
http://www.casia.org/modular/SF/tubevcf.pdf
http://www.casia.org/modular/SF/tubevcf.jpg
It's quarter eurocard, which seemed like an economical format.

softfin · Posted: Fri Jan 11, 2008 2:41 am Post subject:

That's an interesting project for sure!
Do you know any cheap and reliable sources where to buy those 5672 tubes?

etaoin · Joined: Jun 30, 2005 Posts: 761 Location: Utrecht, NL

I got one from Jeroen, but I don't where he got them from.

Packing date March 1958!

softfin · Posted: Fri Jan 11, 2008 3:24 am Post subject:

Ok. I did a quick search and found a couple of sources, although there must be even more.

http://cgi.ebay.de/R%C3%96HRE-TUBE-5672-DL652-DL-652-VALVO-JAN-1958-NOS-NEW_W0QQitemZ320197857180QQcmdZViewItem

http://www.radiotubesupply.com/index.html

Nice to see such old tubes are still available Smile

synthmonger · Posted: Fri Jan 11, 2008 10:30 am Post subject:

What type of resistors does this use? Sorry I'm a newb when it comes to tubes Laughing

etaoin · Joined: Jun 30, 2005 Posts: 761 Location: Utrecht, NL

This is a low voltage tube so bog standard resistors.

Funky40 · Posted: Fri Jan 11, 2008 4:14 pm Post subject:

thanks alot for that links

synthmonger · Posted: Fri Jan 11, 2008 4:29 pm Post subject:

That filter sounds sick! I'm definately going to build this one when I get ahold of some tubes.

zipzap · Posted: Fri Jan 11, 2008 5:06 pm Post subject:

Those samples sound perfect! Love that 12v tube stuff. I´m triying to figure out how it works. WHat about C2 and C3? should be of same value, i guess? Can someone explein what the 130n-130k at the gate of the Fet are doing?

zipzap · Posted: Fri Jan 11, 2008 5:15 pm Post subject:

If you can´t get a 5672 i´m sure most tubes will work somehow in this circuit. raising the voltage to 30v (or +-15) might help if a tube sounds like it´s broken.

j.baars · Joined: Jan 11, 2008 Posts: 16 Location: netherland

Hi everyone,
Its so nice you like my filter design.
if you can't get any tube's , I still have some.
I am working on a design similar to this one,but with an other tube which is more common.
so, soon there will be lots more of synth design.(tubes and semiconductor)
I opened up my 70s design books to publish.
just keep an eye on,
www.synthforum.nl
www.electricdog.eu
www.bfxweb.nl
www.bfxmusic.com
bye,
jeroen baars

blue hell · Posted: Fri Jan 11, 2008 7:52 pm Post subject:

Jeroen.

nog geen tijd gehad om te luisteren helaas, morgen !!

blue hell · Posted: Sat Jan 12, 2008 1:00 pm Post subject:

Luka · Joined: Jun 29, 2007 Posts: 1003 Location: Melb.

andrewF · Posted: Sat Jan 12, 2008 10:04 pm Post subject:

Luka · Joined: Jun 29, 2007 Posts: 1003 Location: Melb.

cheers andrew

andrewF · Posted: Sun Jan 13, 2008 3:26 am Post subject:

Let us know how you go!

Luka · Joined: Jun 29, 2007 Posts: 1003 Location: Melb.

no problem,
it wont be anytime soon but ill definitely give it a shot

zipzap · Posted: Mon Jan 14, 2008 9:30 am Post subject:

Whatever i say, these are only my observations. This is rather experiance than reall knowlege. Please correct me...
i have been experimenting with the 12sh1p. It needs 12V, but only very little current. Although it´s designed for anode voltages around 250V it works good with 30V, giving a gain of about 5-10. Whenever triyng a new tube it is of course important that the heating is correct. Another thing is that the tube won´t like beeing overpowered, but that is hardly gonna happen in designs like this. So just install the tube, make sure the heating is correct, the other connections are made depending on direct or nondirect heating, pentode, triode, etc, and start tweaking the anode and kathode resistors. In Class A designs like this one you want to set those resistors so that with 0V input the output is around half the supply voltage, otherwise headroom will be limited.
For low power, low voltage stuff 10k-100k is a good range for the anode resistor.

etaoin · Joined: Jun 30, 2005 Posts: 761 Location: Utrecht, NL

I've updated my PCB design (links in the first post). Connected an unconnected ground plane, fixed a cap value and changed some hole sizes and the FET footprint.

Sound sample:
http://www.casia.org/modular/SF/tubevcf.mp3

Pic:
Posted Image, might have been reduced in size. Click Image to view fullscreen.

Posted Image, might have been reduced in size. Click Image to view fullscreen.

etaoin · Joined: Jun 30, 2005 Posts: 761 Location: Utrecht, NL

As the VCA is close in design to the VCF, I modified the PCB to make a VCA one This will take both versions (just replace the transistor by a jumper and leave off the 4k7). Check the schematics to see which component values belong to the version you want.

http://www.casia.org/modular/SF/tubevca.jpg

http://www.casia.org/modular/SF/tubevca.pdf

janvanvolt · Joined: Nov 24, 2005 Posts: 285 Location: Mainz, Germany

Will have my pcb ready next week; i have designed a lovely frontpanel for dotcom:

meansuckervcf-panel.gif

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Mean Sucker VCF DOTCOM Frontpanel

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Fernando · Posted: Sun Jan 20, 2008 5:32 am Post subject:

This filter sounds great, thank you!

I also have some 1J24B and 1AG5 tubes , so it would be good to know how to adapt the circuit for them.

niiice sound!

EDIT: it seems that the direct equivalent is the DL69.
Anyhow the 5672 is quite easy to find for $3-$6, plus shipping, of course (some people ask up to $20 only for the tube, sick!) Other theoretical equivalents can be found for $1-$4...

EDIT II: I know it's obvious, but I just realized this filter's crazy resonance can be VC using an external (tube?) VCA

.

Fernando · Posted: Sun Jan 20, 2008 12:02 pm Post subject:

While looking for possible equivalents of the 5672 I looked at the table Andrew pointed.
I looked for heater voltage of 1.25V and 50 mA or less, down to 10mA.
I also looked for same pinout (2E31 pinout).
Then I realized that most of the tubes matching with these specs had a much smaller amplification factor than the 5672.

---> So my question is, for VCFs and VCAs, wich amplifying factor range should be apropiate?
The 5672 has 0.065 W as a reference, but many of them are in the 0.001-0.040 W range...

---> Also, what's the influence of the load (5672 = 20k, others up to 1200k)

.

ickystay · Joined: Nov 15, 2006 Posts: 143 Location: Oregon